Attachment for straight edges



J. F. DOHRWARDT ET AL ,4

ATTACHMENT FOR STRAIGHT EDGES Filed July 12, 1944 KF- U 3nventor John $17 aluwardt: D wot/2.3 MD ahrwandv a (Ittomeg Patented Nov. 26, 1946 OFFICE 2,411,529 ATTACHMENT FOB STRAIGHT EDGES John F. Dohrwardt and Dorothy M. Dohrwardt, Detroit, Mich.

Application July 1 2, 1944, Serial No. 544,532

2 Claims.

1 This invention relates to straight edges used in drafting and particularly to attachments for straight edges.

In moving an ordinary straight edge up and down on a penciled drawing, friction tends to detract from the sharpness of the lines and lead is to some extent transferred over the entire surface of the drawing, detracting from its appearance. If a drawing is being inked the draftsman must exercise great caution in moving the straight edge or wet lines will be blurred.

An object of the invention is to provide a simple and inexpensive attachment for a straight edge that will predeterminedly space it from a drawing in a manner to almost completely eliminate detriment to the drawing.

Further objects are to adapt such an attachment to be readily shifted along the straight edge to the point where it is most needed; to shape the attachment so as to minimize its area of contact with a drawing; and to form the attachment of a material that will give rise to a minimum friction in engaging a drawing.

These and various other objects are attained by the construction hereinafter described and illustrated in the accompanying drawing, wherein:

Fig. 1 is a perspective view of a drawing board, showing several of our attachments applied to a straight edge associated with said board.

Fig. 2 is a fragmentary top plan view of the straight edge and one of our attachments applied thereto.

Fig. 3 is an end View of the same.

In these views, the reference character I designates an ordinary drafting board and 2 the usual straight edge movable up and down on such board.

-Mechanisms for restraining a straight edge from any angular shifting are well known and require no illustration in this connection.

Our attachment consists of an elongated strip of light and very smooth plastic material having its mid portion 3 disposed transversely to and beneath the straight edge and having end portions 4 return-bent to project toward each other above the straight edge, terminally contacting its top face. To facilitate shifting of the attachment and permit of accurately predetermining a pressure exerted on the straight edge by the end portions 4, it is preferred to slightly arch such portions as clearly appears in Fig. 3. Thus the attachment may be manufactured with the ends of its portions 4 spaced above the portions 3 a distance slightly less than is required in use, so that there will be a slight upward springing of the end portions in slipping the attachment over the end of a straight edge, whereby the device acquires a slight yielding grip-on the straight edge to resist its accidental shifting. It is preferred' to form the attachment at its margins with slight rounded beads 5 coextensive with said margins, said beads minimizing the areas of contact with a drawing. Because of their small areas and their very smooth faces, said beads permit of practically no adhesion of lead as the attachment is shifted on a penciled drawing.

The number of the attachments used on any straight edge depends on its length, the requisite being to avoid unsupported lengths of the straight edge adequate to sag into engagement with a drawing. The strip from which the attachment is fashioned may be formed in any desired length by an extrustion or other suitable process, and may be sheared to shorter lengths suitable for our purpose. The thickness of the beaded portions of the strip is preferably about three sixty-fourths of an inch, this being sufficiently less than the standard thickness of drafting triangles and curves that these will not tend to slip beneath the straight edge.

The term straight edge as used in the following claims is inclusive of the blade of a T-square whereon our attachment may be used just as on a straight edged member guided atboth ends.

What we claim is:

1. An attachment for a straight edge comprising an elongated strip of material bent to provide a mid portion for underlying the straight edge and end portions projecting toward each other for overlying the straight edge, said attachment being proportioned to slide freely along the straight edge, said strip being formed on its drawing-engaging face with at least one rib transversely rounded and extending substantially from I straight edge, said strip being formed on its drawing engaging face with spaced marginal transversely rounded ribs substantially cbextensive with said face and affording reduced areas of contact with a drawing.

DOROTHY M. DOHRWARDT. JOHN M. DOHRWARDT. 

